This invention relates to fabrication of solid state structures, and more particularly relates to dimensional control of solid state structural features.
Precise dimensional control of solid state structural features is essential for many applications in fields ranging from biology and chemistry to physics, optics, and microelectronics. The term xe2x80x9csolid statexe2x80x9d is here meant to refer to non-biological materials generally. Frequently the successful fabrication of a solid state system critically depends on an ability to articulate specific structural features, often of miniature dimensions, within very tight tolerances. Accordingly, as solid state systems evolve to the micro-regime and further to the nano-regime, nanometric dimensional feature control is increasingly a primary concern for system feasibility.
There have been established a wide range of microfabrication techniques for producing and controlling structural feature dimensions in micromechanical and microelectromechanical systems. For example, high resolution lithographic techniques and high-precision additive and subtractive material processing techniques have been proposed to enable small-scale feature fabrication. But in the fabrication of many nano-regime systems, in which structural feature dimensions of a few nanometers are of importance, it is generally found that conventionally-proposed techniques often cannot form the requisite nano-scale features reproducibly or predictably, and often cannot be controlled on a time scale commensurate with production of such nano-scale features. As a result, volume manufacture of many systems that include nanometric feature dimensions and/or tolerances is not practical or economical.
The invention provides processes and corresponding process control methodology that enable reproducible and predictable production of structural features for solid state mechanical and electromechanical systems. The processes of the invention can be controlled to produce, control, and/or change feature dimensions in the nano-regime and can include real time feedback control operating on a time scale commensurate with the formation of nano-scale solid state features.
In one technique provided by the invention, for fabricating a feature of a solid state structure, a solid state structure having a surface is provided and is exposed to a flux, F, of incident ions. The conditions of this incident ion exposure are selected based on:                     ∂                  ∂          t                    ⁢              C        ⁡                  (                      r            ,            t                    )                      =                  F        ⁢                  xe2x80x83                ⁢                  Y          1                    +              D        ⁢                              ∇            2                    ⁢          C                    -              C                  τ          trap                    -              F        ⁢                  xe2x80x83                ⁢        C        ⁢                  xe2x80x83                ⁢                  σ          C                      ,
where C is the concentration of mobile adatoms at the structure surface, r is vector surface position, t is time, Y1 is the number of surface adatoms created per incident ion, D is the surface adatom diffusivity, xcfx84trap is the average lifetime of a surface adatom before adatom annihilation occurs at a structure surface defect characteristic of material of the solid state structure, and "sgr"C is a cross-section for surface adatom annihilation by incident ions that is characteristic of the selected ion exposure conditions.
The selected ion exposure conditions control sputtering of the structure surface by the incident ions and result in transport, within the structure including the structure surface, of material of the structure to a selected feature location, in response to the ion flux exposure. This produces the desired feature substantially by locally adding material of the structure to the feature location. This technique can be employed for changing a dimension of, rather than, or in addition to, fabricating a feature at a selected feature location.
xe2x80x9cSolid-statexe2x80x9d is used herein to refer to materials that are not of biological origin. By biological origin is meant naturally occurring, i.e., isolated from a biological environment such as an organism or cell, or otherwise occurring in nature, or a synthetically manufactured version of a biologically available structure, or a synthetic or non-naturally occurring homologue or derivative of a naturally occurring material that substantially retains the desired biological traits of interest. Solid-state encompasses both organic and inorganic materials. The structure can be provided as, e.g., a substrate of inorganic or material, or crystalline material, and can be provided as a semiconductor wafer, a membrane, a layer in which the prespecified feature is to be fabricated, or other suitable structure.
The incident ion flux exposure condition selection can include, e.g., selection of structural material composition, temperature, electronic charge state, electronic doping, and surface defect characteristics, selection of ion flux, energy, species, or time structure, selection of ambient gas species and/or pressure, or selection of the value of another process parameter of the exposure.
The ion exposure conditions can also be selected by carrying out at least one test incident ion exposure of the solid state structure material under selected test incident ion exposure conditions. A physical detection species is directed toward a designated structure location during each test incident ion exposure. Then the detection species is detected in a trajectory from the designated structure location to indicate feature fabrication dependence on the test ion exposure conditions. The ion exposure conditions can then be selected based on the test ion exposure conditions and the corresponding indicated feature fabrication dependence on the test ion exposure conditions.
These processes enable fabrication of a wide range of structural features in a manner that is reproducible, controllable, and efficient. Applications in fields ranging from biology to microelectronics are enabled by these processes, and can be carried out in a manner that is commercially viable. Other features and advantages of the invention will be apparent from the following description and accompanying drawings, and from the claims.